10_18

Materials Science and Engineering: An Introduction

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244 Spheroidite > 0.70 %C <0-1.0 %C Thus, only spheroidite has a composition overlap for both of hardness and ductility restrictions; the spheroidite would necessarily have to have a carbon content greater than 0.70 wt% C. 10.D4 This problem asks us to consider the tempering of a water-quenched 1080 steel to achieve a hardness of 50 HRC. It is necessary to use Figure 10.27. (a) The time necessary at 425 ° C is about 650 s. (b) At 315 ° C, the time required (by extrapolation) is approximately 4 x 10 6 s (about 50 days). 10.D5 We are to consider the tempering of an oil-quenched 4340 steel. From Figure 10.26, for a minimum tensile strength of 1380 MPa (200,000 psi) a tempering temperature of less than 450 ° C (840 ° F) is required. Also, for a minimum ductility of 43%RA, tempering must be carried out at a temperature greater than 400 ° C (760 ° F). Therefore, tempering must occur at between
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Unformatted text preview: 400 and 450 ° C (750 and 840 ° F) for 1 h. 10.D6 This problem asks if it is possible to produce an oil-quenched and tempered 4340 steel that has a minimum yield strength of 1400 MPa (203,000 psi) and a minimum ductility of 42%RA, and, if possible, to describe the tempering heat treatment. In Figure 10.26 is shown the tempering characteristics of this alloy. According to this figure, in order to achieve a minimum yield strength of 1400 MPa a tempering temperature of less that about 425 ° C is required. On the other hand, tempering must be carried out at greater than about 380 ° C for a minimum ductility of 42%RA. Therefore, an oil-quenched and tempered 4340 alloy possessing these characteristics is possible; tempering would be carried out at between 380 ° C and 425 ° C for 1 h....
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This document was uploaded on 05/04/2010.

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